Prepaid services in modern telephone networks allow network operators to issue subscriptions on a prepaid basis. A prepaid service account contains an amount of charging value that can be used to pay for outgoing calls as well as for incoming calls. A prepaid service account can have an expiration date. Calls can be made with the account as long as the call limitations are not exceeded. Examples for call limitations are an empty account or a passed expiration date. Call charges are automatically deducted from the account. The account can be refilled with charging value for continued usage.
Prepaid Services may be offered to customers not wanting a permanent subscription or to customers who for some reason cannot get credit approval. In mobile communications networks, prepaid services are particularly useful for car rental agencies, travel agencies or organisers of fairs and seminars. These companies can in turn supply their customers with the prepaid account.
U.S. Pat. No. 6,029,062 discloses a charging method for a communications service in a communications system, wherein a prepay call management platform which is directly coupled to a telecommunications carrier switch processes a communications service. After detecting for a roaming subscriber a request for a call to be charged on the subscriber's prepayment account, the call is transferred to a home prepay platform of the communications network by sending data to the home prepay platform, which computes a credit information. The credit information is sent to the prepay call management platform, which processes the call according to the credit information.
WO 99/30480 describes a method and system for providing prepaid and credit-limited telephone services. Apart from a real-time telephone call monitoring, rating and response system, it provides a billing system maintaining accounts and associated service profiles for subscribers. The billing system can obtain temporary customer profiles for roamers visiting the service territory of the host telephone service provider. For serving roaming subscribers, customer service information like credit limit and prepaid balance are for each account provided by a roamer clearinghouse, which is a central, regional or nationwide or international database.
In the state of the art, a solution for providing prepaid services in a fixed network is based on the Intelligent Network (IN), as described in WO 98/27715. A prepaid service originating call is routed by the terminal exchange (TE) to a service switching point (SSP), which requests connection time from a prepaid services account kept at a service control point (SCP). The SCP, which analyses the cost of the call and checks the account balance, sends information on the length of the connection time assigned to the call to the SSP and deducts the account in real time during the call. During the connection, the SSP monitors the elapsing of the connection time assigned per request, and when the assigned connection time is less than a specific threshold, an additional time request is sent to the SCP. The SCP updates the account balance, when the connection is terminated.
A cellular communications system can comprise a HPLMN, as well as additionally at least one VPLMN. As designed for a fixed network, the described prepayment method is not suited for a cellular communications system, in which subscribers regularly move within their home public land mobile network (HPLMN) as well as into and within visited public land mobile networks (VPLMNs), because the corresponding roaming is not supported.
As an additional disadvantage, the communications network must support an IN architecture providing SSPs with service switching functions, at least one SCP with-a service control function and a service management point (SMP) with a service management function. All interfaces are vendor specific. Therefore, the interface to access the prepaid service accounts is vendor specific as well, which limits compatibility within the network. Furthermore, the amount and complexity of signalling messages exchanged between SSP and SCP is high. Also, the dialogue between these nodes must be kept during the whole call, which binds network resources. In addition, it is difficult to charge not only the call duration, but also events like supplementary services and short message services (SMS), because the SCP does not get the corresponding signalling information.
As described in Mouly, Pautet, The GSM System for Mobile Communications, ISBN 2-9507190-0-7, chapter 9.1.2, pp 572-577, another method for payment of communications services in GSM is the creation of toll ticketing (TT) records in a mobile switching centre (MSC) and their transfer by tape or electronic transfer to a node controlling user accounts. This method is not real-time oriented, because the service is executed before the TT records are sent to the node that is controlling user accounts and the records arrive always with a certain delay. Therefore, also in the case of electronic transfer of toll tickets there is, for an operator maintaining a prepaid account and depending on the billing strategy for a call, a risk either of overcharging the account or of undercharging due to an empty prepaid account. Although an operator of a HPLMN might take the latter risk, usually a VPLMN operator will not. Therefore, roaming of a prepaying subscriber cannot be granted.
Another known method for prepayment of communications services is to store the subscribers credit on a smart card in the terminal. This method is less convenient to the service provider due to a lack of control and a certain fraud potential. A high effort is necessary to avoid this risk. A smart card-based prepaid system is described in the article ‘Natel D Easy’, ComTec, vol. 2, 1997, p.16-20.